Meeting the energy needs of humans in a sustainable manner is a global challenge. Storage and conversion of energy become increasingly relevant as we move towards greater reliance on renewable or non-traditional energy sources. Devices to store and deliver electricity, in particular, need to be able to efficiently convert chemical energy into electrical energy. Batteries and fuel cells are commercial examples of such devices that are in widespread use today, and that are expected to rise in importance as energy technologies in the future.
Batteries and fuel cells both currently suffer from relatively low energy densities, i.e. the quantity of energy (or power) that can be delivered to a user relative to the weight of the device. Higher power densities in batteries and fuel cells enable longer duration intervals between recharging and increased processing power for portable electronic devices. Furthermore, improved power densities would enable increased-range electric vehicles and distributed energy storage.
Improved power density for batteries can in principle be achieved by making thicker electrodes that contain a larger layer of energy-storage material for batteries. However, these approaches have not been successful. Thick battery materials tend to crack under repeated cycling, which electrically isolates the energy storage material and decreases battery capacity. Additionally, conventional electrodes in current state-of-art battery systems such as lithium-ion batteries comprise a film pressed onto a metal foil current collector. The film is typically formed from a polymer binder, conductive agents such as carbonaceous materials, and active materials. The active material loadings or the thickness of the electrode film is restricted due to the internal resistance increase of the film.
Improved energy density for fuel cells can in principle be achieved by introducing more carbon which yields greater surface area for fuel-cell electrodes. Fuel-cell electrodes are typically made of a compressed powder (carbon particles for conductivity, a catalyst, and a polymer binder) which becomes insufficiently conductive as the electrode thickness increases and the electrons must cross multiple high-resistance carbon particle boundaries. As the electrode is made thicker, the resistance increases and eventually the additional electrode material will lose electrical contact with the current carrier.
In light of these and other shortcomings in the art, improved electrodes are needed for both batteries and fuel cells, to overcome electrode thickness limitations in the art. What is needed is to reduce internal resistance so that thicker and more-efficient electrodes may be fabricated. Improved electrodes are desired to increase energy density and power density, improve heat management, and increase device lifetimes for batteries as well as fuel cells.